Gunite/plaster stains

[Matt 633]

I am currently helping a friend that has let their pool get away from them. Over this last weeked, they drained and refilled their 25K gallon pool. I have been able to help and advise them about the water and it is now under control. The bottom of the pool is very stained - looks dirty. Does anyone have any suggestions other than a complete drain and acid washing? I realize that acid washing is probably better left up to the pros, but we're pretty hands on people that wouldn't mind tackling this.

Thoughts please!

 

[JasonLion]

The first thing to do is to figure out what kind of stains they are. Try lightly rubbing with some crushed Vitamin C tablets in a sock and with a trichlor tablet and tell us what happens. Vitamin C will remove metal stains and trichlor will remove organic stains. If neither works it is probably scale, though there are a couple of other possibilities.

 

[Matt 633]

Many thanks Jason. It isn't metal staining - though there are a few spots in the pool where iron staining is appearant - rusty appearance- looks like something fell to the bottom and started to decompose.

My guess would be organic. It looks like there may have been a solids (algae?) build up at one point and it has left some type of staining after draining. Much like a very bad bath tub ring. The sides look the worst.

I'll try the tri-clor puck this weekend.

Again, many thanks.

 

[Matt 633]

The staining is organic in nature. Tri-chlor will dissolve it pretty well. Upon further evaluation, I would imagine that a good scrubbing and power wash would bring it back to life. Short of draining and doing this, what's the suggested course of action?

 

[Matt 633]

Sorry, I forgot to post the water numbers .

FC 7
CC 0
pH 7.2
TA 120
CH 250
CYA <30, 25 best guess

Thanks

 

[JasonLion]

Bring the pool up to shock level and brush the stained areas several times a day while holding it at shock level. In most cases a day or two of this will take care of the staining. Shock level depends on the CYA level, 12 to 15 with CYA around 25.

If it is actually black algae the stains will usually return unless FC is held at the high end of the normal range, around 6 for CYA of 25. Hopefully it is something else.

 

[Matt 633]

Thanks Jason .